Road traffic crashes and injuries are a major societal challenge around the world. However, the majority of injuries and fatalities occur disproportionately in low-income and medium-income countries. Previous studies have concluded that risky behaviours were the main contributing factor of traffic crashes. Turn signal neglect (TSN) when making a turn is one of those risky behaviours. Unfortunately, research on TSN has been very limited. This study investigates the prevalence of TSN-related crashes and factors affecting TSN among motorcyclists and car drivers. Data was obtained from self-administered questionnaires conducted in Vietnam. The findings showed that 17.54% of motorcyclists and 14.76% of car drivers have experienced at least one crash caused by their failure to turn signals in the last three years. Additionally, fewer years having a riding/driving license, longer daily travelling time, lower frequency of turn signal use, and having received a fine due to TSN were found to be positively associated with TSN-related crashes for both motorcyclists and car drivers. The findings highlight the importance of TSN for road safety and the need for authorities to develop more effective educational strategies and to increase traffic law enforcement.@en